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Message-ID: <87tx0ok7zt.fsf@mid.deneb.enyo.de>
Date: Sun, 21 Dec 2014 22:28:38 +0100
From: Florian Weimer <fw@...eb.enyo.de>
To: oss-security@...ts.openwall.com
Subject: Re: can we talk about secure time?

* Dave Horsfall:

> On Sun, 21 Dec 2014, Florian Weimer wrote:
>
>> [...] but I have the impression that the correct clock changes every 
>> couple of years.
>
> This sounds like you're referring to leap seconds,

No, I meant the recommend time to use in this context.  If
clock_gettime(CLOCK_MONOTONIC) is the right choice, that's good,
because it has vdso accelleration (but I don't know how effective that
is in practice).  On some systems, obtaining time is really painfully
slow. [*]

> where due to the 
> Earth's rotation slowing down (as determined by the International Earth 
> Rotation Service), an extra second is inserted every so often, typically 
> in July; it's quite fun watching it on a GPS receiver (assuming that it 
> even survives the event, as I've seen a few cheaper ones lose the plot).

GPS time does not have leap seconds.

[*] If you upgrade OpenSSL and RAND_bytes is suddenly so much slower,
that's the place to look—upstream mixes not just the PID, but also the
current time into the pool to achieve more complete fork protection.

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